Electrolytic refining or depositing of tin



Patented Aug. 28, 1923.

COLIN G. PINK, OF YONKERS, NEW YORK, ASSIGNOR TO GUGGENHEIM BROTHERS, OF.

7 NEW YORK, N. Y., A COPARTNEBSHIP.

ELECTROLYTIC REFINING 0R DEPOSITING OF TIN.

No Drawing.

To all whom if may concern:

Be it known that I, COLIN G. FINK, a citizen of the United States. residing at Yonkers, in the county of Westchester, State of New York, have invented certain new and useful Improvements in Electrolytic Refining or Depositing of Tin; and I dohereby declare the following to be a full, clear, and exact description of the invent-ion, such as will enable others skilled in the art to which it appertains to'inake and use the same. .7

This invention relates to the electrodeposition of tin and more particularly to the electrolytic refining of tin. Theinvention has as its general object the provision of certain improvements in the electrodeposition of tin, and particularly contemplates the provision of an improved method of refining tin electrolytically in which use is made of an electrolyte from which the tin ]S deposited in a more satisfactory physical condition than by the methods heretofore generally practiced in this art.

Considerable dilliculty has heretofore been encountered in the electrodeposition and in the electrolytic refining of tin on account of the tendency of the tin to deposit from the electrolyte in the form of longcrystals which build up into Ftrees or projections and eventually short-circuit the electrodes. Various expedients, such as *diaphragins, electrolytes of special composition, etc, have been suggested from time to time for overcoming this difliculty, but, as far as I am aware, the problem has not heretofore been satisfactorily solved from a practical standpoint. Diaphragms are objectionable because they introduce an added complication into the electrolytic cell, and their eliminas tion is, of course, desirable. Such electrolytes as have heretofore been suggested for the electrodeposition of tin, while they do in certain instances overcome the formation of trees on the cathode, possess, nevertheless, other disadvantages, such, for example, as commercially unstable or expensive electrolytes (oxala-te's, fluosilicates, etc.) as Well as deposits of. impractical physical form.

Tin is deposited from neutral or alkaline Application filed February 1, 1922. Serial No. 533,249.

electrolytes in a finely granular orspongy gen ions (for example, hydrochloric acid or a suitable chloride) have been used to a considerable extent in theelectrodeposition of tin. In general, I have found that such acid electrolytes containing halogen ions give rise to very 1on crystals of tin which build up into trees and short-circuit the electrodes after a comparatively short time of operation. Certain organic addition agents when introduced into such a halogencontaining electrolyte will reduce the size of the deposited tin crystals, but large quantities of addition agents are required to produce deposits which can be readily handled in practice without mechanical loss.

As the result of my investigations and researches, I have found that a satisfactory smooth' coherent deposit of tin can be obtained under commercial operating condi tions by electrolyzing and aqueous bath. containing an appropriate tin compound and a preponderating concentration of sulfate ions and a preponderating concentration of ions of a metal more electropositive than tin, such as sodium, magnesium, iron, titanium or aluminum. The electrolyte which I use in practicing the invention is an aqueous solution containing, for the most part, sulfuric acid, tin sulfate and. an alkali, alkaline earth, or other suitable sulfate. Thiselectrolyte contains apreponderating concentration of sulfate ions (anions), that is to say,

sulfate ions, such, for example, as chlorine,

' deposit of fluorine, etc. lln addition, the electroylte employed in practicing the present invention contains a .preponderatlng concentration of ions of a metal more electropositive sodium or other metal more electropositive.

than tin for each ion of tin in the electrolyte (assumin for convenience in explanation and definition complete disassociation of the salts in solution).

In actual practice, an electrolyte of substantially the following composition has given excellent results:

' 233 grams Glaubers salt (Na SO,.10H,O) per liter.

1.50 grams sulfuric acid per liter.

35 grams tin per liter.

2 grams aloin per liter.

in general, the principal substances in the foregoing electrolyte may be varied in about the following proportions:

Glaubers salt (Na,S0,.1OH O) 50-350 grams per liter.

Concentrated sulfuric acid 50-150 grams per liter.

Tin 12-40 grams per liter.

Aloin 1-3 grams per liter.

In each of the foregoing formula: the tin present in the electrolyte is calculated as metallic tin, although it is probably present in the electrolyte as stannous sulfate (SnSOQ.

It is very probable that the sodium sulfate and the stannous sulfate form a double salt structurally resemblin the alums.

Sulfuric acid alone 18 not well adapted for use in tin-containin electrolytes, because with such an electro yte a very crystalline tin is roduced. Furthermore, sulfuric acid alone 18 inoperative in the case of tin anodes containing appreciable quantities of lead as impurity. Sodium sulfate, on the other hand, when used alone in a tin- 7 containing electrolyte tends to give aspongy deposit of tin. owever, when sulfuric acid and sodium sulfate are used together in the tin-containing electrolyte, .the aforementioned defects of each substance alone are so neutralized that a dense, hard, finely crystalline deposit of tin is obtained.

if prefer to use sodium sulfate or Glaubers salt in preparing the electrolyte for carrying out the present invention because of its availability and cheapness. However, the sodium sulfate may be replaced either'wholly or in part by magnesium sulfate, iron sulfate, aluminum sulfate, or by any sulfate of us a metal more electropositive thantin. Thus,

aeearae the electrolyte may contain sodium and magnesium sulfates, .or sodium, magneslum, and

* iron sulfates, or sodium, iron and chromium Aloin is a glucoside obtained from aloes and varies more or less in chemical composition and physical properties according to the source from which it is obtained. It is chiefly prepared from Curacao aloes.

Aloin, as an addition agent in tin electrolytes, assists in preventing the formation of needle-like crystals.- Instead of aloin, similar glucosides or organic colloids, such for example, as saponin, digitalis, cascara sagrada, cresylic acid, henna, gelatin, glue, tannic acid, or the like, may, if desired, be used as the addition agent. However, of a large number of addition agents with which I have experimented, aloin is the most satisfactory, and I therefore prefer to employ this substance in some form or other (for example, in the form of an extract from Ouracao aloes) in the practice of the present invention. Gelatin and cresylic acid-soap emulsion, as addition. agents, have temporarily produced very satisfactory electrolytic deposits of tin, but the activity of these agents appears to be quickly destroyed. On the other, hand, aloin, as an addition agent, remains active for a relatively long period of time. Moreover, aloin may be cheaply obtained from Curacao aloes, the hot water extract from Curacao aloes containing the desired essential constituents of aloin and to nearly the same extent.

Very satisfactory practical deposits of tin are obtained at room temperature from electrolytes of the general composition hereinbefore discussed. In general, temperatures around 20 centigrade have been found entirely satisfactory. Temperatures lower than 20 C. cause a further refinement in the crystalline grain of the deposited tin, but such further advantages are of little material value in commercial practice. Temperatures much above 20 C. cause coarsening of the crystalline grain anda tendency towards irregularity of the deposit. In general, satisfactory results are secured when the temperature of the electrolyte is between 15 to (1*(60-80 F.)..- On account of the low electric potential and consequent low I heating effect of the current it is not diflicult to maintain the electrolyte at 15 to 25 C.

In practicing the invention, impure tin is made the anode and the cathode may advantageously bemade up of tin foil. No diaphragms are required in the electrolytic cell. The voltage required is low; a voltage drop of around 0.2 volts, or even less, being satisfactory. The current density may advantage ously be about 10 amperes per square foot.

The method of electrodepositing tin in accordance with the present invention is one of marked economy in current consumption, and in addition gives Ersatisfacfactory tin deposit. Moreover, the method of the invention can be continuously practiced over long periods of time without objectionably short-circuiting the electrodes.

The main advantages of electrodepositing tin in accordance with the method of the invention may be briefly summarized as follows:

1. Relatively low cost of the electrolyte.

2. Firm, dense, finely crystalline deposit of tin which makes it possible to turn out relatively thick cathodes Without treeing and short-circuiting of electrodes.

3. No artificial heating of electrolyte is required, ordinary room temperatures being satisfactory.

4. No diaphragms are required.

5. The impurities in the anode tin, such as antimony and bismuth, form sludges which are easily removed.

The method of the present invention is well adapted for use in the electrolytic refining of tin produced by the reduction of oxidized tin ores with a gaseous reduction agent, such as hydrogen, carbon monoxide, or the like, at relatively low temperatures, as described in my application for Letters Patent of the United States Serial No. 452,- 951 filed March 17, 1921. Where the reduced tin is recovered in metallic state, for example, as cast impure tin, such cast tin can be used as the anode in the electrolytic refining process. If the reduced tin is of a porous or a granular character, it may be compressed and then used as the anode.

The impurities contained in anodes produced as described in the preceding para graph from Bolivian tin ores will vary somewhat, but usually lead, bismuth and antimony are present in appreciable amount, and small amounts of arsenic, iron and copper may also be present. The impurities, particularly the bismuth and antimony, tend to remain behind on the anodes or to form a sludge which settles to the bottom of the electrolytic apparatus.

As previously stated, small amounts of chlorides, fluorides. or the like, present in the electrolyte of the invention, are not prejudicial to the final result. The amount of such substances present in the electrolyte will, however, always be relatively small in comparison with the amount of sulfate ions present in the electrolyte because, in accordance with the main principle of the present invention, the electrolyte contains a preponderating concentration of sulfate ions and may or ma not, as the case may be, contain relative y small amounts of other El W anions, such as chlorides, bromides, fluorides,

and the like. In addition, the electrolyte of the invention contains a preponderating con- 7 centration of ions'of a metal or metals more electropositive than tin.

Where the crude anode tin contains around 2% or more of lead, I find it of advantage to employ reduced amounts of sulfuric acid sideration thatas high acidity as possible be used in order to keep the power costs down. A further objectionable feature of low acidity is the tendency-for spongy deposits to form on the cathode. Likewise, it has been found advantageous with high lead anodes to reduce the concentration of the Glaubers salt to one-half or one-fourth the 233 grams per liter hereinbefore recommended. The Glaubers salt' may be re-v placed by other salts such as ferrous sulfate. without greatly impairing the quality of the cathode deposit, yet greatly improving the anode corrosion. I have found that from about 50 to about 100 grams perliter oi Glaubers salt gives the best results as regards anode corrosion and cathode deposition.

I have also found that the addition to the.

electrolyte (hereinbefore. described) of certainmetal sulfates (herein called additional metal sulfates) such as sulfates of iron, titanium, cobalt, nickel, manganese and chromium, produce a beneficial result.

These metal sulfates appear to play a two fold part in the tin-refining cell. In the first.

place, their presence has the efi'ect of loosening the slimes coating from the anode, thus rendering corrosion of the anode more easy. In the second place, the presence of these metal sulfates effects a marked improvement in the density, hardness and blend of the tin crystals deposited on the cathode. This has been found. especially true of nickel, iron and chromium. I have secured satisfactory results by the addition to the electrolyte of 10 to 20 grams of iron (in the form of ferrous sulfate) or 1 to 3 grams of chromium (in the form of chromous sulfate) per liter,

fates is particularly beneficial in case the anodes contain lead and bismuth as high as 2% or 3%. If the anode tin is very impure and carries much over 3% lead. i prefer to give the molten tin a preliminary treatment before casting into anodes. Blowing the molten anode tin with oxygen or air will reduce the lead content very easily. Addition of sulfur to the molten bath has a similareffect. However. I find that the most reliable procedure, giving uniformly d results during refining later on, is to a d to themolten anode tin bath from 0.1% to 1.5% aluminum metal; The ratio of lead to tin should be approximately ten to one. I

have found that lead tin anodes containing as much asten per cent of lead and about two polarization bismuth would give rise tono voltages during the course of tin; the ano'ie would dissolve irregularities in the The presence of the per cent of refining the completely without any voltage performance.

aluminum'metal in slimes to be comparatively loose, and any lead sulfate formed during electrolysisdoes not cling to the face of the anode as is likely to be the case in the absence of aluminum. Other metals besides aluminum have been tried but the results are not anywhere as good.

I claim': 1. The improvement in the electrodeposition of tin, which comprises depositing the tin from an electrolyte containing a preponderating concentration of sulfate ions with respect to other anions therein and a concentration of ions of a metal more electropositive than tin preponderating with respect to other cations therein.

2. The improvement in the electrodeposition of tin, which comprises depositing the tin from an electrolytecontaining a preponderating concentration of sulfate ions with respect toother anions therein, and a concentration of sodium ions exceeding the concentrati n of tin ions therein. I

3. The improvementin the electrodeposition of tin, which comprises depositing the tin from an electrolyte containing a prep'onderating concentration of sulfate ions with respect to other anions therein and a concentration of magnesium ions exceeding the concentration oftin ions therein.

4. The improvement in the electrodeposition of tin which'comprises depositing the tin from an electrolyte containing a preponderating concentration of sulfate ions with respect to-other anions therein and containing aconcentration of sodium and magnesium ions preponderating with respect to other cations therein.

5. The'improvement in theelectrodeposition of tin, which comprises depositing the tin from an electrolyte containing a preponderating concentration of sulfate ions with rename the tin anode causes the respect to other anions therein and a preponderating concentration of sodium ions.

with respect to other cations therein.

6. The improvementin the electrodeposition of tin. which comprises, depositing the tin from an electrolyte containing sulfuric acid and sodium sulphate in preponderating amounts as compared with the amounts of other substances contained in the electrolyte.

7. The improvement inthe electrodeposition of tin, which comprises depositing the tin from an electrolyte containing sulfuric acid and the sulfate of a metal or metals more electropositive than tin in preponderat ing amounts as compared with the amounts pf other substances contained in the electroyte.

8. The improvement in the electrodeposi- .tion of tin, which comprises depositing the tin from an electrolyte containing in each liter thereof from 50-150 grams of sulfuric acid and from 50-350 grams of Glauberssalt. 1

9. Theimprovement in the electrodeposit on of tin, which comprises depositing the 13m from an electrolyte containing a preponderating concentration of sulfate ions with respect to other anions therein, and a concentration of ions of a metal more electropositive than tin preponderating with respect to other cations therein and also con taining aloin as an additionagent.

10. The improvement in the electrodeposition of tin, which comprises depositing the tin from an electrolyte containing sulfuric acid and the sulfate of a metal or metals more electropositive than tin in substantially the following proportions: Sulfuric I acid 50 to 150 grams, metal sulfate or sulfates, the molecular equivalent of 50 to 350 grams of Glaubers salt per liter.

11. The improvement in theeieetrodeposition of tin, which comprises depositing the tin from an electrolyte containing from 50 to 150 grams per liter of sulfuric acid and from 50 to 350 grams per. liter of" the sulfate of a metal or metals more electropositive than tin and up to 30 grams per liter (calculated as metal) of one or more of the hereinbefore mentionedadditional metal sulfates.

12. The method of refining tin electrolytically which comprises depositing the tin from an electrolyte containing sulfuric acid and sodium sulfate.

13. The method of refining tin electrolytically, which comprises depositing the tin from an electrolyte containing sulfuric acid and magnesium sulfate.

14. The method of refining tin electrolytically, which comprises depositing the tin from an electrolyte containing stannous sulfate, sulfuric acid, sodium sulfate and an addition agent.

15. The method of refining tin electroof low voltage from an impure .tln anode to a cathode, the electrolyte containing stannous sulfate, sulfuric acid, sodium sulfate,

5 and aloin.

16. The method of refining tin electrolytically which comprises subjecting reduced tin oreto compression, placing the tin thus compressed in an electrolytic bath, and passing a current through said compressedtin, 10 V the electrolyte and a cathode. r

; 17. Ar -anode 'for use in the electrolytic refining of tin, comprisingcompressed, relatively impure, reduced tin ore.

In testimony whereof I aflix 'm COLIN FINK.

signature. I 

